Maintenance of a viable airway is critical to patient safety during surgical procedures conducted under general anaesthetic. Maintenance of a viable airway during such surgical procedures had, for many years, been achieved by insertion of an endo-tracheal tube into the patient. The endo-tracheal tube was typically inserted through the oral cavity or nasal cavity, into the larynx, through the vocal cords and into the trachea. As the endo-tracheal tube had to be inserted through the vocal cords, difficulty was often experienced in correctly positioning the endo-tracheal tube.
British patent no. 2,111,394 (which corresponds to U.S. Pat. No. 4,509,514) describes a device for maintaining an airway in a patient. The device is described as being an artificial airway device. The device comprises a curved, flexible tube opening at one end into the interior of a hollow mask portion shaped to conform to fit readily into the actual and potential space behind the larynx and to seal around the circumference of the laryngeal inlet without penetrating into the interior of the larynx. Commercial forms of this device have an inflatable collar extending around the periphery of the mask. The inflatable collar is adapted to form the seal around the laryngeal inlet when the collar is inflated. Additionally, the mask portion included an inflatable posterior part which is adapted to press against the back of the throat and thereby increase the sealing pressure around the laryngeal inlet.
British patent no. 2,111,394 states that the shape and (when fitted) the inflatable part or parts of the mask ensure that it approximates closely to the shape of the space between the laryngeal inlet and the walls of the lower part of the throat behind it. Since the walls of tissue forming the back of the throat are relatively rigid, inflation of the mask forces it more tightly against the tissues surrounding the laryngeal inlet, so forming an airtight seal, while tending to anchor the mask in position.
In use of the device described in GB 2,111,394, the device is inserted through the mouth of the patient and down the throat past the epiglottis until the mask comes to rest with its distal end in the base of the throat, lying against the upper end of the normally closed oesophagus. The inflatable ring on the mask is then inflated to seal around the inlet to the larynx. The patient's airway is thus secure and unobstructed and the laryngeal mask can be connected directly to conventional anaesthetic circuit hosing for either positive pressure or spontaneous breathing.
When a patient is placed under general anaesthetic, the patient is frequently lying in the horizontal position on his or her back or side. When under general anaesthetic, reflex response in the body is suppressed and the sphincter closing the top of the stomach from the oesophagus is relaxed. Consequently, gastric juices (which are acidic in nature) can flow along the oesophagus. It is important to ensure that such gastric juices do not enter the trachea as aspiration of gastric juices into the lungs can have potentially fatal consequences.
Similarly, where a patient under general anaesthetic is undergoing a surgical procedure of the nose, mouth or throat (e.g. a tonsillectomy, endoscopic nasal surgery), saliva, blood and nasal secretions can travel down through the laryngo pharynx and into the trachea and thereafter into the lungs. Again, this is a potentially dangerous situation.
When using a laryngeal mask such as the one described in British patent no. 2,111,394, the present inventor has found that if significant volumes of gastric juices collect around the mask the gastric juices can work their way past the seal of the mask and into the larynx. This is dangerous if the gastric juices and acid gets into the lungs.
The laryngeal mask described in British patent no. 2,111,394 may also have problems of leakage occurring in the inflatable ring or collar, due to a faulty valve in the pilot line or due to leakage or tearing of the inflatable ring or collar. It is apparent that deflation of the cuff substantially increases the chance that the seal around the larynx will be lost, which consequently increases the possibility of gastric acids getting into the lungs. Even in normal use without cuff deflation, there remains a possibility that a gush of acid from the stomach can get around the cuff and enter the air passage as there is no other way for the acid to escape (due to the cuff totally blocking the laryngopharynx). The presently available masks also have the limitation that they cannot be used safely on all patients, especially patients with a large abdomen.
In order to minimise the likelihood of the abovementioned problems, the patentee of British patent no. 2,111,394 introduced a laryngeal mask that had a double cuff to produce a total seal around the area of the larynx. This mask also included an additional tube that extends along the back of the laryngeal mask and extends into the oesophagus. This allows gastric acid to be sucked out from the stomach by way of a Ryles tube inserted through this passage. It has been found that applying suction to the oesophageal tube of this laryngeal mask can cause the tissue of the oesophagus to be sucked into the inlet of the second tube. This results in the second tube becoming blocked, thereby preventing removal of gastric acid from the upper oesophagus.
The double cuff laryngeal mask also includes two small additional tubes that open into the larynx-side of the mask. These tubes can be used to remove from the larynx any gastric juices that make their way past the seal into the larynx. However, applying suction to these tubes raises the possibility of removing anaesthetic gases from the trachea and increases the possibility of collapsing the lung or lungs. Successful removal of all the volume of acid coming up from the stomach is also not possible. Consequently, the acid may preferably move into the large diameter airway (trachea) due to the large diameter of the airway providing a path of lower resistance to fluid flow than the smaller diameter opening in the mask and also because the trachea bronchial tube is at a lower level in a supine patient.
The improved laryngeal mask described above is described in Australian patent no. 630433.
In our International patent application no PCT/AU2004/001011, the entire contents of which are herein incorporated by cross reference, we describe a device for maintaining an airway in a patient comprising a mask, the mask having a resilient conformable peripheral portion shaped such that the mask forms a seal with the larynx when the mask is positioned in the laryngo pharynx to thereby prevent ingress of extraneous fluids into the larynx, the peripheral portion of the mask defining at least one cavity for providing fluid communication between the laryngo pharynx and the oesophagus when the mask is inserted into the laryngo pharynx, and an airway tube connected to or formed with the mask for passing gas to the larynx when the mask is properly inserted into the laryngo pharynx.
This device, in preferred embodiments, does not have an inflatable cuff around its periphery. Rather, the walls of the mask are made from a resilient material and the walls themselves comprise a design in which the walls extend outwardly and then upwardly and inwardly. In this fashion, the walls assist in obtaining a seal around the larynx to prevent fluid from the oesophagus entering the larynx during anaesthesia. Further, the mask also has cavities that provide fluid communication between the laryngo pharynx and the oesophagus when the mask is inserted into the laryngo pharynx.
Although laryngeal masks such as the examples described above have found wide acceptance, difficulties can be encountered during insertion of the laryngeal mask into the airway of the patient. In particular, during insertion of the laryngeal masks, the tip of the masks has often been found to come into contact with the pharynx. This necessitates extra manipulation of the mask during insertion in order to properly position the mask in the patient.
The anatomy of the head and neck of humans includes numerous muscles, nerves and cartilages. The thyroid cartilage comprises an open and, generally semi-cylindrical cartilage that extends around the anterior of the upper part of the trachea. Located below the thyroid cartilage is the cricoid cartilage. The cricoid cartilage forms a solid ring of cartilage that extends around the upper part of the trachea. The posterior part of the cricoid cartilage is located in the wall between the trachea and the oesophagus.
The cricoid cartilage, being in the form of a solid ring or closed ring of cartilage, is used to close off the oesophagus in patients who have a possible full stomach and who require emergency surgery or who have stopped breathing. In these instances, either an endotracheal tube or a laryngeal mask is inserted into the patient in order to provide airway ventilation. However, as the patient may have a full stomach, the risk of regurgitation or vomiting is enhanced. Therefore, external cricoid pressure, in which pressure is applied externally from the anterior part of the neck to the cricoid cartilage to compress the oesophagus against the posterior pharyngeal wall, is used to include the upper oesophagus to stop regurgitated material from entering the glottic area to prevent aspiration into the lungs. The external cricoid pressure must be applied and maintained until the time that a viable airway is fully secured. It has been found, in order to successfully apply intermittent positive pressure ventilation (IPPV) using presently available laryngeal masks, external cricoid pressure is necessary. To perform an effective external cricoid pressure requires extra trained personnel.
In our international patent application number PCT/AU2008/001259, the entire contents of which are incorporated herein by cross reference, we describe a device for maintaining an airway in a patient. The device comprises a mask having a peripheral portion that forms a seal with the larynx when the mask is positioned in the laryngo pharynx to thereby prevent ingress of extraneous fluids into the larynx, and an airway tube connected to or formed with the mask for passing gas to the larynx when the mask is properly inserted into the laryngo pharynx. The peripheral portion of the mask includes a soft, flexible portion that contacts tissues surrounding the laryngeal opening when the device is inserted into a patient, the soft, flexible portion being arranged whereby application of pressurised gas to the airway tube urges the soft, flexible portion into contact with the tissues surrounding the laryngeal opening or the pharyngeal wall.
The device described in our international patent application number PCT/AU2008/001259 has been subjected to a number of trials. In an article published in the Journal of Obstetric Anaesthesia and Critical Care, 2012, Volume 2, Issue 1, pages 23 to 30, trials were conducted which evaluated the “first attempt” and “overall insertion” success rates, insertion time, ease of insertion and removal of the device, oropharyngeal leak pressure, and anatomical position at fiberoptic view. The “first attempt” success rate was high (88%) and “overall insertion” success rates was considered “easy” to “very easy” by the operators in 92% of patients. Removal of the device was considered easy in all cases. The oropharyngeal leak pressure was above 30 cm H2O in all patients and a maximum of 40 cm H2O was achieved in 82% of the patients.
These results indicate that the mask is easy to insert into a patient and that a strong seal can be formed around the structures of the larynx. As a result, a viable airway can be established by most practitioners using the mask. However, the present inventor has developed modifications to the laryngeal mask to provide an even better success rate for insertion of the mask into a patient to establish a viable airway and to achieve a very high seal pressure of about 50 cm H2O.